encoding DVD audio AC3(446kbps) to AAC

[se4923]

I know that AC3 is 5.1 channel
but I don't know what's gonna happen when I encode to AAC
would it be reduce to 2 channel ?
and what bitrate should I use? to maintain quality of audio.

thank you

[linyx]

Use BeLight, it has good presets for 5.1 AAC encoding.

[lexor]

Well the downmix might depend on which GUI you are using, but encoders by themselves won't enable downmix options, so the number of channels is preserved.

Bitrate is usually a function of your final file size, you give it as much as you can after you know how much the video takes. I find that for my ears 64kbps/channel (so 384kbps total for 5.1) is indistinguishable from 448 and 640 AC3 source (this is one of those cases, where mathematically there is a loss in quality, but practically you don't hear it). It all depends on you though, so give it a listen, this is just a place to start.

[tebasuna51]

With BeLight (or BeHappy) you can decode the ac3 selecting if downmix (to stereo) or not, apply DRC (not recommended to preserve the Dynamic Range) and other settings.
Also you can select the aac encoder, I recommend you use the NeroAacEnc with VBR q=0.4 (to transcode ac3 the range 0.3-0.5 can be appropriate)